This project involves characterization of two proteins involved in Hg detoxification, MerR and MerA. MerR is the regulatory protein, controlling expression of the rest of the Mer proteins and MerA is the mecuric ion reductase. These proteins play a key role in bacterial Hg detoxification. We will determine what (if any) affect the binding of MerR to DNA has on the Hg site structure. We will compare the Hg site structure with the structures found when Zn, Cd, and Co are bound at the Hg site, in order to address the question of why other metals, that also bind to MerR, do not stimulate transcription. In addition, we will explore the interactions between metal sites ( i.e., Zn will bind to the Hg-MerR -- does this affect the structure?). Our present data, coupled with the known coordination chemistry of Hg(II), suggests that MerR has a trigonal planar site. We will use polarized experiments to test this proposition and to determine the orientation of the Hg site relative to the DNA. Previous work has shown MerA to have a Hg(cys) 2 structure when saturated with Hg. We will characterize the Hg site as a function of Hg loading and NADPH in order to test the alternating sites hypothesis of MerA function.